<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>改变输出流</title>
</head>
<body>
    <p>hello</p>
    <p>hello</p>
    <p>hello</p>
    <p>hello</p>
    <p>hello</p>
    <p>hello</p>
    <button onclick="demo()">按钮</button>

        <script>
            function demo() {
                document.write("world");
            }


        </script>
</body>
</html>